1. Field of the Invention
This invention relates to an automatic document feeding apparatus for use in a copying machine, a filing apparatus having an image reading apparatus (scanner), an image forming apparatus, having an image filing section capable of document filing and copying, and the like.
2. Description of the Related Art
Today, an automatic document feeder (ADF) is widely used in a copying machine, a filing apparatus, an image forming apparatus with a filing section, or the like, to copy or store a great number of documents (images) at high speed. The ADF saves a user from setting documents on a document reading plane of an image reading apparatus one by one and from changing documents to others. The ADF also saves a user from reversing a document on the document reading plane when both sides of the document are copied or stored. Furthermore, a user can perform any other operation during the copying or memorizing of documents, resulting in greater operational efficiency.
An ADF generally includes a document tray, a document pickup unit, a separation/feed unit, an aligning unit, a transporting unit, a discharge unit, and a discharge tray.
An ADF having the above constitution performs the following operations. Documents set in the document tray are picked up by the pickup unit and sent to the separation/feed unit. The documents are then separated one from another by the separation/feed unit. Each document is fed to the aligning unit in which any skew of the document to its transporting direction is removed. After that, the document is transported by the transporting unit to a predetermined position of a document reading plane of a reading apparatus or a copying machine. Image information, such as characters and graphs, is read out from the document by the reading apparatus or copying machine, and the document is discharged from the discharge unit onto the discharge tray. This operation is repeated until all the documents are fed from the document tray.
An example of such an ADF is disclosed in, for example, U.S. Pat. No. 4,954,848.
In ADFs, there is fear that two or more documents are picked up from the document tray when they are stacked one on another. To eliminate this problem, most of them incorporate a separation/feed unit for separating documents one from another. However, the documents cannot always be separated owing to their thicknesses and conditions such as cohesion (adsorption), folding, and curving, even though the separation/feed unit is prepared. To resolve this problem, ADFs include a stacked-document detector for detecting two or more documents which are supplied with them stacked one on another. when the detector detects stacked documents, it stops the ADF.
However, the ADF including the stacked-document detector has the drawbacks that, when the detector detects stacked documents, a user has to stop his operation and reset the documents himself or herself. If the user is away from the ADF, the ADF remains stopped.